Exposure to electromagnetic fields can cause interference or damage to electronic equipment, causing that equipment to malfunction or rendering it nonoperational. This is particularly a risk in the case of sensitive computing system data, which can be corrupted or lost in the event of a strong electromagnetic pulse or intentional electromagnetic interference event (EMP/IEMI).
EMP/IEMI events typically take one of two forms. First, high field events correspond to short-duration, high voltage events (e.g., up to and exceeding 100 kilovolts per meter), and typically are of the form of short pulses of narrow-band or distributed signals (e.g., in the frequency range of 1 MHz to 10 GHz). These types of events typically generate high voltage differences in equipment, leading to high induced currents and burnout of electrical components. Second, low field events (e.g., events in the range of 0.01 to 10 volts per meter) are indications of changing electromagnetic environments below the high field damaging environments, but still of interest in certain applications.
Existing electromagnetic systems use electrical antennas to detect the existence of a high-field or low-field event. For example, electrical dipole antennae, D dot detectors, or electro-optical detectors can be used. Electrical dipole antennae typically operate using a Schottky-type diode detector system, which receives signals directly based on the induced voltage at the antenna. D dot detectors measure the time rate of change of electrical displacement, and deduce the electrical field strength at an antenna by integrating the time rate of change of an electrical field over a set amount of time. As such, these detectors also operate directly on the electrical field. Electro-optical detectors use changes of an index of refraction in a solid or liquid based on the presence of an electromagnetic field.
These systems have drawbacks. This is because each of the above types of antennas and associated circuitry either cannot respond to events across the entire expected signal range of high field and low field events, or is too expensive or unreliable for use in certain environments. In the case of a high field event (e.g., a high voltage pulse or other event having a large signal intensity, as explained above), the various electrical antennae described above observe a large electrical field, resulting in a large induced voltage on the antenna. Additionally, common mode current flowing on the outer surface of an antenna probe or attached cable can cause unpredictable variations in the output power or voltage produced by the antenna. This can cause potential damage to downstream circuitry. Even in the case of low field events, it can be difficult to adequately capture events over the entire signal range of expected frequencies (e.g., 1 MHz to 10 GHz). Furthermore, it can be difficult to manage a high voltage antenna configuration in the proximity to sensitive electronic equipment to be protected, particularly if that electronic equipment is intended to be shielded from large electronic signals.
For these and other reasons, improvements are desirable.